arq-docs: canned demo built on Arq-Signals snapshot-example

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Sub-issue of #6. Build on Arq-Signals examples/snapshot-example/: sample snapshot in, hand-authored illustrative findings (9-field shape) out, clearly labelled as a sample. No live engine, no Analyzer/Workbench code, no real detection output.

Acceptance: demo shows input→output shape with synthetic fixtures; clearly marked illustrative.

[fheikens]

⚠ Deferred / patent-review required. A patent is still to be filed. Do not document detection/diagnosis techniques, mechanisms, anything about spoofing, or how findings are derived. Stay at or below current elevarq.com depth. This item is held until the patent is filed or the maintainer clears it. See #6.